This invention relates to the field of musical instrument construction. It is especially relevant to, but not limited to banjo construction.
The physics of sound generation are complex and largely beyond the scope of this invention. I will, however, describe the differences between sound producing parts of an instrument and those parts whose primary function is structural. The purpose of this explanation is to fully understand the objects and advantages of this new instrument construction.
Most stringed musical instruments have a soundboard mounted to a rim. These parts are meant to actively participate in generating and defining the sound of an instrument. The soundboard, rim and usually a sound reflecting back are the main resonating components of a stringed instrument. String vibrations are transmitted through a bridge and to the soundboard. As the soundboard is set in motion by the string vibration, the sound is amplified by its large resonating surface. The soundboard, rim and back all resonate and define an air space that also resonates. I will call the sound producing parts acoustic members. A resonant chamber is defined as the assembled acoustic members and resulting air space defined therein.
Structural members as distinct from acoustic members, would be those parts with a primarily structural purpose. Examples would include the following; top bracing of a guitar to provide support for string attachment, hardware for securing and tensioning a drum or banjo's soundboard, a neck providing a rigid connecting point for the strings, and a tailpiece providing a rigid connecting point for the other end of the strings.
In current practice it is not possible to isolate the acoustic members from the structural members. All members are secured together so sound vibrations from an acoustic member will pass to the structural members. In fact, the structural members can effect the overall sound substantially. Ideally they should not add distorting vibrations or dampen the desirable acoustic vibrations. The banjo example will illustrate some of the problems encountered when designing an instrument with good structural and acoustic properties.
The rim of a banjo is an important acoustic member but it also must bear the stresses of the neck, string and soundboard attachments. The direct contact between the neck and rim can absorb and impede the rim's natural resonance. Also the rim structure can yield to the neck's distorting string tension and warp. In this case the neck angle changes leaving the strings uncomfortably far from the neck's playing surface. Most banjos, therefore, employ one or two reinforcing rods installed across the rim's diameter. Adjustment of the rods can help a rim retain its circular shape resulting in proper neck angle and correct string height. The problem is that tightening these rods will also impart sound dampening stresses to the rim. The resulting sound is often too thin and weak, especially in the lower frequency range.
Typical banjo construction employs many parts to tension the membrane style soundboard. Multiple tension hooks are positioned around the perimeter of the instrument's body. It is necessary to take extreme care in tightening each tension hook uniformly to avoid membrane breakage. Assembly and proper attainment of membrane tension is extremely time consuming and requires a degree of skill.
Some "top tension" banjo designs of the past attempted to simplify the task of soundboard or head installation and maintenance. They offered multiple tensioning screws that were adjustable from the top of the instrument. Numerous other tension adjusting mechanisms were devised in the prior art of banjo construction but nearly all involved tightening multiple fasteners around the instruments' perimeter.
As mentioned previously, banjo necks are usually attached to the rim assembly via reinforcing rods or dowels. They are fastened to the neck and pass across the rim's diameter. One rod usually goes through the opposite side of the rim and is secured with nuts on either side of the rim. Adjustment of the rods or nuts will deflect the shape of the rim. This distortion enables slight neck angle and string height adjustability. Over-adjustment can lead to dampened or restricted tone and damage to the instrument. There is a need for a better neck connection that puts no distorting stress on the acoustic members but allows for a wider range of adjustability.
Banjos exist with any number of strings but currently the most popular style is the five string banjo. The fifth string is usually attached to a tuning peg which is protruding out from the side of the neck. The fifth string's shorter length is necessary to achieve a high pitch without breaking. This peg can often get in the way while playing, especially if the player uses his thumb to fret strings. Another shortcoming of this peg is that it is stationary. Certain tunings may call for lower or higher pitch on the fifth string. Without a means to change the string's length, adequate pitch adjustment is impossible. The neck widens on the side of the neck where the fifth string starts. The overall shape of the neck is therefore asymmetric. This makes it impossible for a right-handed instrument to be restrung for use by a left-handed player.
In some instruments such as the European Zither-Banjo, a portion of the fifth string passes through a tunnel in the neck from the fifth fret to the peghead. This method allows tuning at the peghead without the cumbersome fifth string peg, but does not solve any other of the above problems and is difficult to manufacture.
Another problem which relates to the necks of stringed instruments such as guitars and banjos is the inconvenience associated with using a capo. A capo is a bar device used to shorten the effective length of the scale in order to play in different keys more easily. The capo's clamping pressure down on the strings makes the instrument slightly out of tune. Frequent retuning is required when affixing or removing a capo. Besides minimizing the tuning problems, it is also desirable to minimize the time required to engage a capo. Many attempts have been made to make them more effective and convenient. The Shubb adjustable capo, U.S. Pat. No. 4,250,790 is an example of one of the more sophisticated designs. The fifth string of a banjo is usually capoed five frets up the neck, separately from the main capo. Devices such as small hooks driven into the neck or some other type of bar mounted clamp that slides along the side of the neck are normally used. Shubb's Capo For Five String Banjo U.S. Pat. No. 3,834,267 is one such sliding single string capo. All clamp-down style capos, including fifth string capos, tend to over-sharpen the strings and take time to adjust. Most capos also tend to become lost if not permanently affixed to the neck.